One resident in Parkland tweeted: "Major liquefaction in Parklands, just a river of it flowing in the garden."

A Radio New Zealand reporter in the suburb of Bexley, where many houses have been "red-stickered" and were lying empty from the previous quake, said there was fresh liquefaction, new flooding and potholes opening up in the road.

Christchurch International Airport has been evacuated along with all the malls in Christchurch. The airport was due to reopen at 4pm, after the runway and building structures had been checked.

Herald reporter Jarrod Booker said the 5.3 aftershock which struck around 3.19pm shook cars from side to side on the tarmac, and was one of half a dozen to strike the city following the intial earthquake. He described the intial quake as "violent".

Civil Defence has activated the National Crisis Management Centre with Cantabrians advised to expect further aftershocks and to "drop, cover and hold on" each time a quake is felt.

The intial quake was felt as far away as Mosgiel, near Dunedin, and in Westport, Hokitika, and Timaru. The 5.3 aftershock was felt in Wellington.

Police say one person has been injured at Eastgate Mall , but they expect more injuries. St Johns reports 19 minor injuries, as at 3pm.

Associate Canterbury Earthquake Recovery minister shaken

Meanwhile Associate Minister for Canterbury Earthquake Recovery, Amy Adams, was among those shaken by this afternoon's first quake.

"I'm not in the central city, I'm out near Darfield in the electorate, but it was bad enough here it had us diving under tables and grabbing each other," she told APNZ.

"It's not what anyone needs at the end of a stressful year and heading into Christmas, and with the memory of the big shake of Boxing Day last year very fresh in our minds."

Demolition manager for the Canterbury Earthquake Recovery Authority, Warwick Isaac told Radio New Zealand most of the buildings in Christchurch had been evacuated.

"Most of the buildings in town, and as I understand, in the suburbs have been evacuated as a precautionary measure.

"The rockfall issue is very much a live issue as rockfall has occurred again, and the liquefaction [is also an issue]."

Eyewitness accounts

Cracks have appeared on the Christchurch Casino building following today's earthquake, an eyewitness said.

Commercial cleaner Daniel Yeoh was having lunch at a Thai restaurant across the road from the casino when the quake struck, and he said he saw cracks appear on the building when sharp aftershocks followed the initial tremor.

"The whole building was shaking, and I was worried that it might just collapse," said Mr Yeoh, who fled soon afterwards.

In the Avonhead Mall food fell off the shelves at the Countdown supermarket and staff ushered people outside.

Actress Robyn Malcolm tweeted: "F*** that was terrifying. My hat goes off to you Cantabrians. Kids and I shaky as."

Logan McMillan, a 30-year-old film maker, said there was some panic in the city following the big shake.

"I'm only on the north side of the city and it felt like a five.

"The way it started out, it felt like it was going to be a serious one.

"We haven't had a shake for a few months.

"The noises that come with, it starts with little shake before it hits in."

"I have friends down at the mall and they said there was stuff falling off the shelves and ceiling panels falling in.

"Everyone evacuating. There's a bit of panic. They said it's chaos down there."

A Sumner resident reports "lots of breakages" and has headed down to the beach for safety.

A caller to Newstalk ZB said the quake was "as vicious" as the February 22 quake that killed 181 people.

"The first thing I felt was a little movement and I said 'what's this?' and I said to my wife 'get under a doorframe somewhere safe'. I just dived under the bench," the caller said.